I didn't say new bitcoin. 'Lost key' coins are currently out of circulation. Degradation of prior encryption standards by quantum computing would lead to those coins returning to circulation (through network compliant transactions) and would return the "in circulation" total to nearer 21,000,000. 

Key holders own the coins. They are not stolen if another person can reasonably calculate the private key; e.g. low entropy dice or brain wallets getting spent. For this reason, I wouldn't time lock coins for added security to dates where I consider quantum computing to be a concern.